Method of joining at least four heat transfer plates to a plate package, and a plate package

ABSTRACT

The application discloses a method of joining at least four heat transfer plates ( 2 ) to a plate package for a plate heat exchanger. Each heat transfer plate ( 2 ) comprises an outer edge portion ( 10 ) extending around the heat transfer plate in its edge area and an inner edge portion ( 11 ) extending around the heat transfer plate inside the outer edge portion ( 10 ). The heat transfer plates ( 2 ) are joined in pairs at a first contact plane to at least two plate pairs ( 16 ) along said inner edge portions ( 11 ). An outer edge portion of one of said plate pairs is brought to abutment at a second contact plane ( 20 ) to an outer edge portion of another of said plate pairs. The outer edge portions ( 10 ) are welded. The application also discloses a plate package produced in this manner.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present refers to a method of joining at least four heat transferplates to a plate package for a plate heat exchanger, wherein each heattransfer plate comprises an outer edge portion extending around the heattransfer plate in its edge area and an inner edge portion extendingaround the heat transfer plate inside the outer edge portion, andwherein the method includes the steps of: joining the heat transferplates in pairs at a first contact plane to at least two plate pairsalong said inner edge portions, bringing an outer edge portion of one ofsaid plate pairs to abutment at a second contact plane to an outer edgeportion of another of said plate pairs, and welding said two outer edgeportions to each other by means of a weld joint.

The invention also refers to a plate package of joined heat transferplates for a plate heat exchanger, in which each heat transfer platecomprises an outer edge portion extending around the heat transfer platein its edge area and an inner edge portion extending around the heattransfer plate inside the outer edge portion, wherein the heat transferplates are joined in pairs to at least two plate pairs along said inneredge portions at a first contact plane and wherein one of said platepairs is welded at a second contact plane to an adjacent of said platepairs along said outer edge portion by means of a weld joint.

Each heat transfer plate in such a plate package is usually providedwith four through-going holes, so-called port-holes. The heat transferplates abut each other in such a manner that the port-holes form fourport channels through the plate package and that two sets of heattransfer passages are formed between the heat transfer plates. Each heattransfer passage is connected to two of the port channels.

Such plate packages are comprised by a plate heat exchanger throughwhich two heat exchanging fluids are intended to flow; one through eachof the two sets of heat transfer passages and associated port channels.

It is essential for the function of such a plate heat exchanger that theplate package is sealed in such a manner that no heat exchanging fluidsmay leak out of the plate heat exchanger in which the plate package iscontained. When the plate package is joined in the manner initiallydefined, satisfactory possibilities are offered to check the tightnessof the plate package. The tightness may be checked in each plate pairprior to being joined by means of said weld joint. When the plate pairshave been welded to each other the tightness of the whole plate packagemay be tested. If then any untight weld joint appear it is accessiblefor correction from the outside of the plate package.

EP 578 933 and GB 580 368 disclose a plate heat exchanger comprisingheat transfer plates which firstly have been joined by welding andthereafter to plate packages.

The plate heat exchanger disclosed in EP 578 933 comprises heat transferplates which firstly are welded in pairs to cassettes about two of thefour port-holes of the heat transfer plates and along edge portions ofthe heat transfer plates. Thereafter, the cassettes are brought toabutment to each other and the heat transfer plates are welded about thetwo other port-holes and along outer edge portions of the heat transferplates. The latter weld joints in the outer edge portions are shaped asedge welds.

GB 580 368 discloses a plate heat exchanger which comprises heattransfer plates permanently joined by resistance welding. The heattransfer plates are firstly welded to each other in pairs to plate pairsalong inner edge portions and thereafter the plate pairs are welded toeach other along outer edge portions.

JP 7-214 319 discloses a method of welding heat transfer plates whichare provided with port-holes by means of edge welds. The heat transferplates are welded to each other along edges of the port-holes by meansof a TIG-weld. The heat transfer plates are held during the welding inpairs about the port-holes by means of a special device which also leadsheat from the welded area in order to avoid heat deformations.

Modern weld methods with a high energy beam, such as electron beamwelding or laser welding, have many advantages from a productions pointof view. Such methods are for instance well suited for automaticmanufacturing and result in weld joints having a high and uniformquality. In connection with welding of heat transfer plates to a platepackage, the greatest advantage of such modern weld methods is the lowpower generation merely subjecting the heat transfer plates toinsignificant heat deformations. WO93/15369 describes a plate heatexchanger comprising a plate package of heat transfer plates which havebeen welded together by laser welding. One heat transfer plate at thetime is welded to the plate package to be formed in such a manner thatevery second heat transfer plate is welded along inner edge portions andevery second heat transfer plate is welded along outer edge portions.The outer edge portions are located between the inner edge portions andthe edges of the heat transfer plates. In addition, each heat transferplate comprises a strengthening bending outside the outer edge portion.However, this known method has the disadvantage that a satisfactorycheck of the tightness is difficult to obtain. Practically, it is tooinefficient to perform a tightness check after the welding of each heattransfer plate. Instead, a tightness check is made when the whole platepackage or an essential part thereof, for instance 10-30 heat transferplates, has been welded together. If a weld joint between the inner edgeportions thereby is not completely tight, this weld joint is practicallynot any longer repairable and the whole plate package or the module hasto be thrown away. Consequently, this method of manufacture requires ahigh process security in the production if one is to obtain anacceptable level of rejection. In order to obtain such a processsecurity, extensive testing and adjustment of the different processparameters are required for each material quality. Consequently, thisweld method is expensive for the manufacturing of plate heat exchangersin small series or in less usual materials.

However, welding by means of a high energy beam is by the techniqueavailable today not possible to utilise for the method initially definedsince a heat transfer plate of a plate pair, which is not to be weldedto a heat transfer plate in an adjacent plate pair, shades the heattransfer plates to be welded together. A nozzle for a high energy beamand a shielding gas surrounding the beam are in addition too large to behoused between two heat transfer plates in a plate pair. Thereby, it hasbeen proposed to form the weld joint as an edge weld. However, it isvery difficult to focus a high energy beam on the edge end surfaces ofthe heat transfer plates if, for instance, the joint is not preciselystraight or if there is a small gap between the plates in the joint.

SUMMARY OF THE INVENTION

The object of the present invention is to remedy the problems mentionedabove and provide an improved weld joint between plate pairs to bewelded together to a plate package for a plate heat exchanger.

This object is obtained by the method initially defined, which ischaracterised in that said weld joint is produced by means of a highenergy beam directed towards one of said outer edge portions at adistance from the outer edge thereof and at an angle other than.perpendicular with respect to said contact plane. Such a concentratedhigh energy beam, for instance a laser beam or an electron beam, mayfocus in a vary accurate manner on one of the edge portions of the platepairs, which means that the weld joint formed will extend through bothof the adjacent edge portions and ensure a connection of highreliability and quality. In addition, the checking possibilities offeredby the method initially defined may be utilised completely. It has beenfound that a high energy beam may penetrate both the outer adjacent edgeportions and produce a weld joint extending through these portions evenif the high energy beam does not hit the surface of the edge portion bya right angle. In such a manner, one may in a simple and elegant wayutilise a nozzle defined above for a high energy beam regardless of itsdimensions. Thereby, the high energy beam may be directed by means of amember and at least one of the member and the heat transfer plates ismoved in relation to each other in such a manner that the member isguided along the outer edge portion beside the heat transfer plates.

According to an embodiment of the invention, essentially each heattransfer plate is provided with four port-holes, wherein two of theport-holes are surrounded by first portions and the two other port-holesare surrounded by second port portions, the heat transfer plates in saidplate pairs being joined along the first port portions before the platepairs are welded to each other. According to an advantageous embodimentof the invention, said plate pairs may then be welded to each otheralong the second port portions by means of a high energy beam directedtowards one of said second port portions at an angle other thanperpendicular with respect to said contact plane. In such a manner aweld joint of a high reliability and quality is obtained also in thiscase. Thereby, said high energy beam may be directed by means of amember guided around the second port portion.

According to a further embodiment of the invention, at least four platepairs are stacked onto each other to a plate package and welded to eachother in an order differing from the order by which the plate pairs arestacked in the plate package. In such a manner, at least initiallyabutting plate pairs will not be welded immediately after each other butfrom a first plate pair said member will be moved to a second platepair, wherein a number of plate pairs are located between the first andthe second plate pairs. By such a method, one may avoid deformations ofthe final plate package due to the thermal tensions arising during thewelding.

According to a further embodiment of the invention, said high energybeam is a laser beam. The object is also obtained by the plate packageinitially defined, which is characterised in that said weld joint isproduced by means of a high energy beam and has, seen in a cross sectionthrough said outer edge portions, a central line forming an angle otherthan perpendicular to the second contact plane. Such a weld joint has ahigh quality and ensures a high reliability with respect to thetightness of the plate package.

Advantageous embodiments of the plate package are defined in thedependent claims 11 to 14. Said angle may advantageously be between 50°and 70°, preferably about 60°.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now to be explained more closely by means ofone embodiment described by way of example and with reference to thedrawings attached, in which

FIG. 1 discloses a plate heat exchanger having a plate package accordingto the present invention,

FIG. 2 discloses a plane view of a heat transfer plate of the platepackage,

FIG. 3 discloses a cross-sectional view of a plate pair of the platepackage,

FIG. 4 discloses a cross-sectional view of two such plate pairs beingwelded according to the invention,

FIG. 5 disclose in a cross-sectional view how the heat transfer platesare welded by means of a laser tool, and

FIG. 6 discloses in a view from above how the heat transfer plates arewelded by means of a laser tool.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

FIG. 1 discloses a type of plate heat exchanger 1 comprising heattransfer plates 2 which are joined to a plate package 3 by welding bymeans of the method according to the present invention. The platepackage 3 is tightened between two support plates 5 and 6 by means oftie bolts 4. One of the support plates 5 is provided with fourconnecting pipes 7, only two of which are disclosed in FIG. 1. Via theconnection pipes 7, two heat transferring fluids are intended to flowthrough the plate heat exchanger 1 in a manner known per se.

A heat transfer plate 2, contained in the plate package 3, is disclosedin FIG. 2. The heat transfer plate 2 has been pressed to haveprotrusions and depressions, partly for forming a press pattern 8 on thecentral parts of the heat transfer plate 2 over which the heattransferring fluids are intended to flow and partly for forming contactsurfaces along which the heat transfer plate 2 is joined to adjacentheat transfer plates 2 in the plate package 3. Along the outer edge 9 ofthe heat transfer plate 2, a first outer edge portion 10 extends, whichin FIG. 2 is illustrated as a continuous line even if the outer edgeportion 10 has a certain width. Inside the outer edge portion 10, asecond inner edge portion 11 extends, which in FIG. 2 is illustrated bya dotted line and which also may have a certain width. The edge portions10, 11 are located at different levels, see FIGS. 3 and 4. Furthermore,the heat transfer plate 2 is provided with four port-holes 12′, 12″,13′, 13″, which are surrounded by essentially plane port portions 14′,14″, 15′, 15″, which also are illustrated as dotted and continuouslines, respectively, and extend around a respective port-hole. The portportions 14′ and 14″ are located at the same level as the inner edgeportion 11 and the port portions 15′ and 15″ are located at the samelevel as the outer edge portion 10, see FIGS. 3 and 4.

When a plate package 3 is to be manufactured by heat transfer plates 2,the heat transfer plates 2 are firstly joined together two and two toplate pairs 16, see FIG. 3. This joining is performed, according to theembodiment disclosed, by means of laser welding. However, it is to benoted that for this joining also other joining methods may be utilised,preferably any one which makes use of a high energy beam, for instanceelectron beam welding. It is also possible to utilise for instanceresistant welding. During this welding of the heat transfer plates 2 toplate pairs 16, the heat transfer plates 2 are turned to be brought toabutment to each other at a first contact plane 17 along the inner edgeportions 11 and along two of the port portions 14′ and 14″ about theport holes 12′ and 12″. The heat transfer plates 2 are welded togetherin the port portions 14′ and 14″ by means of weld joints 18 and alongthe inner edge portions 11 by means of weld joints 19. After the platepair 16 has been welded, the weld joints 18 and 19 are checked withrespect to the tightness. If any plate pair 16 is not completely tight,the weld joint 18, 19 in question may thereby be welded once again in asimple manner.

FIG. 4 discloses a section through four heat transfer plates 2, i.e. twoplate pairs 16 of the plate package 3. Two adjacent heat transfer plates2, one from a respective plate pair 16, are brought to abutment to eachother at a second contact plane 20 along the outer edge portions 10 ofthe heat transfer plates 2 and joined by means of a weld joint 21. Saidtwo adjacent heat transfer plates 2 also abut each other at the secondcontact plane 20 along port portions 15′ and 15″. These port portions15′, 15″ have ben joined by means of a weld joint 22.

As appears from FIG. 4, the weld joints 21 and 22 are inclined in across-section in relation to the contact planes 17 and 20. A centre linec extends through each of the weld joints 21, 22 in such a manner thatthe distance between the centre line c and the outer edge of the meltedzone of the respective weld joint 21, 22 is equal at each side of thecentre line c. In particular, each centre line c forms an angle α and β,respectively, other than perpendicular to the contact planes 17, 20.According to the present invention, the weld joints 21 and 22 areproduced by means of a concentrated high energy beam, for instance alaser beam or an electron beam, which has been directed obliquelytowards the outer edge portions 11 and port portions 15′ and 15″,respectively, of the heat transfer plate 2 in order to avoid shadingedges of an adjacent heat transfer plate 2 in the same plate pair 16.Said angle a is between 50° and 70°, preferably about 60°. It is to benoted that also other values of said angle α, β are possible, however itis essential that the angle is such that the edges of an adjacent heattransfer plate 2 do not shade the outer edge portions 10 and portportions 15′, 15″, respectively, without the high energy being able tofocus on the surface of these portions.

When a plate package 3, comprising two or more plate pairs 16, has beenwelded together along the weld joints 21 and 22, the tightness of thewhole package 3 may be checked. If the plate package 3 is not tight, anyof the weld joints 21 and 22 is leaking since the weld joints 18, 19previously were found to be tight when the individual plate pairs 16were checked. Consequently, if the plate package 3 is not completelytight, the weld joints 21, 22 in question may thereby be welded onceagain in a simple manner. The plate package 3 may then be mountedbetween the two support plates 5 and 6 in the plate heat exchanger 1.FIG. 5 and 6 discloses schematically how the weld joints 21 and 22 maybe produced by means of a laser weld tool 23. The laser weld tool 23comprises a laser 24 schematically disclosed and nozzle 25. The nozzle25 is arranged to direct a shielding gas and the laser beam at a slopingangle α, β towards the outer edge portions 10 and towards the portportions 15′, 15″ respectively. Furthermore, the laser tool 23 comprisestwo press wheels 26 which are arranged to engage between each other toadjacent outer edge portions 10 and to adjacent port portions 15′, 15″,respectively, in order to position and compress these. In FIGS. 5 and 6,laser tools both for welding of the outer edge portions 10 and forwelding of the port portions 15′, 15″ are disclosed. However, it is tobe noted that practically it may be difficult to perform these weldingoperations simultaneously. In order to avoid thermal deformations of theplate package, the plate pairs 16, in addition, are to be weldedtogether in another order than the order in which the plate pairs 16 arestacked onto each other in the plate. package 3 disclosed. For instance,the tool 23 and/or the plate package 3 are moved in such a manner thatthe tool 23 is moved firstly along the two lowermost plate pair 16 anddirectly thereafter along the two uppermost plate pair 16.

The present invention is not limited to the embodiment disclosed but maybe varied and modified within the scope of the following claims.

What is claimed is:
 1. A method of joining at least four heat transferplates (2) to a plate package (3) for a plate heat exchanger (1),wherein each heat transfer plate (2) comprises an outer edge portion(10) extending around the heat transfer plate (2) in its edge area andan inner edge portion (11) extending around the heat transfer plate (2)inside the outer edge portion (10), and wherein the method includes thesteps of: joining the heat transfer plates (2) in pairs at a firstcontact plane (17) to at least two plate pairs (16) along said inneredge portions (11), bringing an outer edge portion (10) of one of saidplate pairs (16) to abutment at a second contact plane (20) to an outeredge portion (10) of another of said plate pairs (16), and welding saidtwo outer edge portions (10) to each other by means of a weld joint(21), wherein said weld joint (21) is produced by means of a high energybeam directed towards one of said two outer edge portions (01) at adistance from the outer edge (9) thereof and at an angle (a) other thanperpendicular with respect to said contact plane (20).
 2. A methodaccording to claim 1, wherein the high energy beam is directed by meansof a member (23, 25) and at least one of the member and the heattransfer plates is moved in relation to each other in such a manner thatthe member is guided along the outer edge portion (10) beside the heattransfer plates (2).
 3. A method according to claim 1 essentially eachheat transfer plate (2) is provided with four port-holes (12′, 12″, 13′,13″), wherein two of the port-holes (12′, 12″) are surrounded by firstport portions (14′, 14″) and the two other port-holes (13′, 13″) aresurrounded by second port portions (15′, 15″), and the heat transferplates (2) in said plate pairs (16) are joined along the first portportions (14′, 14″) before the plate pairs (16) are welded to eachother.
 4. A method according to claim 3, wherein said plate pairs (16)are welded to each other along the second port portions (15′, 15″) bymeans of a high energy beam directed towards one of said second portportions (15′, 15″) at an angle (β) other than perpendicular withrespect to said contact plane (20).
 5. A method according to claim 4,wherein said high energy beam is directed by means of a member (23, 25)guided around the second port portion.
 6. A method according to claim 3wherein the first port portions (14′, 14″) of the heat transfer plates(2) in said plate pairs (16) are brought to abutment to each other atthe first contact plane (17) before said joining of the plate pairs(16), and that the second port portions (15′, 15″) of adjacent platepairs (16) are brought to abutment to each other at the second contactplane (20).
 7. A method according to claim 1 wherein at least four platepairs (16) are stacked onto each other to a plate package (3) and weldedto each other in an order which differs from the order in which theplate pairs (16) are stacked in the plate package (3).
 8. A methodaccording to claim 4 wherein said high energy beam is a laser beam.
 9. Aplate package of joined heat transfer plates (2) for a plate heatexchanger (1), in which each heat transfer plate (2) comprises an outeredge portion (10) extending around the heat transfer plate (2) in itsedge area and an inner edge portion (11) extending around the heattransfer plate (2) inside the outer edge portion (10), wherein the heattransfer plates (2) are joined in pairs to at least two plate pairs (16)along said inner edge portions (11) at a first contact plane (17) andwherein one of said plate pairs (16) is welded at a second contact planeto an adjacent one of said plate pairs (16) along said outer edgeportion (10) by means of a weld joint (21), wherein said weld joint (21)is produced by means of a high energy beam and has, seen in across-section through said outer edge portions (10), a centre line (c)which forms an oblique angle (α) to the other contact plane (20).
 10. Aplate package according to claim 9, wherein essentially each heattransfer plate (2) is provided with four port-holes (12′, 12″, 13′,13″), wherein two of the port-holes (12′, 12″) are surrounded by firstport portions (14′, 14″) and the two other port-holes (13′, 13″) aresurrounded by second port portions (15′, 15″), and the first portportions (14′, 14″) of said heat transfer plates (2) in said plate pairs(16) are joined to each other.
 11. A plate package according to claim10, wherein adjacent second port portions (15′, 15″) of two of saidplate pairs (16) are welded to each other by means of a second weldjoint (22) which is produced by means of a high energy beam.
 12. A platepackage according to claim 11, wherein the second weld beam (22) seen ina cross-section through said second port portions (15′, 15″) has acentre line (C) which forms an angle (β) other than perpendicular tosaid contact plane (20).
 13. A plate package according to claim 12,wherein said angle (β) is between 50° and 70°.
 14. A plate packageaccording to claim 13, wherein said angle (β) is about 60°.
 15. A platepackage according to claim 9, wherein said angle (α) is between 50° and70°.
 16. A plate package according to claim 15, wherein said angle (α)is about 60°.